Do they have lockers where you could put the cooler? Or maybe pack a ton of ice into it and leave it in the car? I have learned it is not a good idea to not have a plan.
Also, I understand about it being hard when your husband is around. My hubby has gotten better since actually realizing he was going to have to change his eating habits if he wanted me to be healthy. But he still does give in when he shouldn't, because eating out isn't a huge deal for his body.
Good luck! I hope you can figure something out!